1. Field of the Invention
The present invention relates to an image display apparatus which has an atmospheric pressure resistant support structure.
2. Description of the Related Art
Among image display apparatuses using electron-emitter devices, a thin flat display apparatus has recently attracted attention as an apparatus to replace a cathode-ray tube display apparatus because of its space-saving and light-weight characteristics.
Such a flat display apparatus includes a hermetic container in which a rear plate having an electron-emitter device and a face plate having an emission member (phosphor) irradiated with an electron beam to emit light, are bonded together via a frame member. The inside of the hermetic container is held in a vacuum of about 10−4 Pa. Image display apparatuses having large surface areas require the use of a mechanism for preventing deformation or destruction of the rear and face plates caused by a pressure difference between the inside of the hermetic container and the outside thereof. Accordingly, the hermetic container in these cases includes a structure support (spacer or rib) made of glass or the like, disposed therein, to support atmospheric pressure. Thus, a distance between the rear plate having a multibeam electron source and the face plate having a phosphor film is normally maintained to be within the range of sub-millimeters or several millimeters, and the inside of the hermetic container is held in a high vacuum as described above. The spacer must not much affect an orbit of electrons flying between the rear and face plates. A cause that affects the electron orbit is a static or dynamic electric field change which results owing to the presence of the spacer by charging near the spacer. Charging of the spacer may be attributed to the emission of secondary electrons from the spacer caused by entry of some electrons emitted from an electron source or electrons reflected on the face plate into the spacer, or the sticking of ions generated as a result of ionization by electron collision.
When the spacer is positively charged, the electrons flying near the spacer are drawn to the spacer, causing a distortion of a displayed image near the spacer. The influence of the charging becomes more conspicuous as the distance between the rear and face plates becomes larger.
Generally, to curb the charging, charges on the spacer are removed by providing conductivity to a surface of the spacer and supplying some currents thereto.
Examples of such display apparatuses are disclosed in Japanese Patent Application Laid-Open Nos. 10-326583 and 2002-237268 (corresponding to European Patents EP 866491 A and EP 1220273 A, respectively). In the JP 10-326583 A, as countermeasures against an undesirable discharge between rear and face plates, a configuration is described in which an anode electrode is divided on the face plate into strips and the strips are connected to a common electrode linked to a high-voltage power supply via a resistor. Also described is a method of electrically connecting the face plate to a spacer.
For the purpose of weakening an electric field of an area (nondisplay area) in which an anode electrode is not formed, JP 2002-237268 discloses a configuration in which an anode electrode and a guard electrode regulated at a potential lower than the anode electrode are disposed on a face plate and in which a resistor film is electrically connected to the anode and guard electrodes. With this configuration, an electric field of an area between the guard electrode and a frame portion is weakened, thereby preventing an occurrence of discharge caused by a shape of a member arranged in the nondisplay area. This display apparatus also includes a spacer which has a resistor film coated on a base material, and the anode and guard electrodes are electrically interconnected.
As described above, in JP 10-326583 A and JP 2002-237268 A, in addition to the anode electrode, various electrodes may be arranged on the face plate on which the anode electrode has been disposed. Such various electrodes can include a common electrode (105) in the case of JP 10-326583 A, and a potential regulated electrode (1015) in the case of JP 2002-237268 A. On the other hand, the spacer disclosed in JP 10-326583 A and 2002-237268 A has an atmospheric pressure resistant structure, and the arrangement of the spacer over the anode electrode and other various electrodes is contemplated so that an atmospheric pressure resistant function can be implemented in various places of a vacuum panel of the display apparatus. As described in JP 10-326583 A and JP 2002-237268 A, in addition to the function as the atmospheric pressure resistant structure, the spacer is required to counter-act charge-up. For this purpose, a charging prevention film on a surface of the spacer is disclosed. However, when the spacer is arranged over the anode electrode and various electrodes as described above, the spacer plays the role of a conductive path which electrically interconnects the anode electrode and various electrodes. Therefore, there is a demand for a better design which not only forms a charging prevention film on a surface of a spacer but also gives consideration to electric behaviors arising between an anode electrode and various electrodes.